Join curves with Python by color
I hope that this script may help you, just pick the curve that has the "guide" color and run the script.

import bpy
import mathutils

#set custom color

#color = mathutils.Color((1,0,0))

#or

#use active's object diffuse color

color = bpy.context.active_object.active_material.diffuse_color

for obj in bpy.data.objects:
    if obj.type == 'CURVE':
        curve = obj
        if curve.active_material.diffuse_color == color:
            curve.select = True
        else:
            curve.select = False


if (bpy.ops.object.join.poll()):
    bpy.ops.object.join()